The present invention relates to hearing devices for aiding the hearing impaired and the profoundly deaf, and more particularly to a water-resistant microphone subassembly providing isolation from case-born vibrations, and wide band frequency response, for use in a Behind-The-Ear (BTE) hearing system. Such BTE system may form part of a cochlear stimulation system.
Cochlear stimulation systems are known in the art. Such systems are used to help the profoundly deaf (those whose middle and/or outer ear is dysfunctional, but whose auditory nerve remains intact) to hear. The sensation of hearing is achieved by directly exciting the auditory nerve with controlled impulses of electrical current, which impulses are generated as a function of transduced acoustic energy. The acoustic energy is picked up by a microphone carried externally (not implanted) by the person using the device and converted to electrical signals. The electrical signals, in turn, are processed and conditioned by a signal receiver and processor, also referred to as a Wearable Processor (WP), in an appropriate manner, e.g., converted to a sequence of pulses of varying width and/or amplitude. The sequence of pulses, or command words that define such sequence of pulses, is carried by an external cable running from the WP to an external headpiece positioned on the side of the patient""s head. A magnet in the headpiece holds the headpiece in place on the head of the user. Such magnet also aligns the headpiece with a corresponding magnet in the an Implantable Cochlear System (ICS). Such ICS receives the command words or pulse sequence, and converts them to appropriate stimulation current pulses that are applied to the auditory nerve through an electrode array implanted in the cochlea, as is known in the art.
While known ICS systems have succeeded in providing the sensation of hearing to the profoundly deaf, they unfortunately also have the disadvantage of appearing unsightly due to the external cable running from the WP to the headpiece positioned on the side of the user""s head.
The WP is typically worn or carried by the user on a belt or in a pocket. While the WP is not too large, it is likewise not extremely small, and hence also represents an inconvenience for the user. The cable which connects the WP with the headpiece is often a source of irritation and self-consciousness for the user.
The above-described aesthetic considerations and inconvenience of an external wire are addressed by U.S. Pat. No. 5,824,022, issued Oct. 20, 1998, for xe2x80x9cCochlear stimulation system employing Behind-The-Ear (BTE) Speech Processor With Remote Control.xe2x80x9d The ""022 patent teaches a small single external device that performs the functions of both the WP and the headpiece. The external device is positioned behind the ear to minimize its visibility, and requires no cabling to additional components. The ""022 patent is incorporated herein by reference.
While the BTE device taught by the ""022 patent resolves the issues of aesthetics and inconvenience, the resulting device, and known BTE hearing aids, disadvantageously expose the microphone to perspiration and rain, resulting in frequent failures. Therefore, there is a need for a microphone assembly that provides resistance to moisture, while maintaining a good frequency response.
The present invention addresses the above and other needs by providing a moisture-resistant microphone subassembly for Behind-The-Ear (BTE) hearing devices, with a substantially flat frequency response to 10 KHz. The microphone subassembly is comprised primarily of a microphone, a boot, and a moisture-resistant membrane. The microphone has an transducer aperture through which sound waves enter the microphone. The boot includes a microphone cavity and a sound port. The boot structurally supports the microphone, provides the microphone with isolation from vibrations in the case of the BTE device, and provides a seal against moisture seeping around the microphone body and into the transducer aperture of the microphone. The membrane resides in the microphone cavity between sound port and the transducer aperture, and resists the passage of moisture, while permitting sound waves to reach the transducer aperture.
In accordance with one aspect of the invention, a boot provides structural support to the microphone. The boot is made from a high compliance material and isolates the microphone from vibrations that might otherwise create false signals. In the absence of such isolation, events such as rubbing the case of the BTE device against hair or skin, could produce undesirable signals.
It is a feature of the present invention to provide a boot which includes a sound waves port and an microphone cavity. The microphone is situated in the microphone cavity. The fit of the microphone inside the microphone cavity provides a seal against moisture. The sound waves port connects with the microphone cavity to provide an acoustic path for sound waves (acoustic waves) to enter the transducer aperture of the microphone.
It is an additional feature of the present invention to provide a means for retaining the microphone in the microphone cavity. In one embodiment, the boot includes boot fingers at the rear of the microphone cavity. Once the microphone has been pushed into the microphone cavity, the boot fingers hold the microphone in place. In another embodiment, the boot includes a retaining flange around the rear of the microphone cavity. The compliance of the boot material allows the retaining flange to stretch to allow the microphone to be pushed into the microphone cavity. Once the microphone is in the microphone cavity, the retaining flange closes around the rear of the microphone to retain the microphone in the microphone cavity.
It is a further feature of the invention to provide a moisture-resistant membrane. The membrane separates the microphone from the environment and prevents moisture from reaching the microphone, but allows sound waves to reach the microphone. In a preferred embodiment, the membrane provides a stable, flat, wideband acoustic frequency response for the microphone subassembly. Advantageously, the resulting response is flat to beyond 10 KHz.
It is additionally a feature of the present invention that the microphone subassembly fit within a cavity of a BTE case. The cavity is located inside a front surface of the BTE device case, and includes a microphone port in the front surface to allow sound waves access to the microphone subassembly. A water deflector or shield is located just above the BTE sound port to deflect water from the microphone port.